This invention relates to a combustor to be incorporated in a gas turbine plant or a combined cycle power generation plant, and more particularly, to a combustor for a gas turbine adapted to substantially reduce density of nitrogen oxides (NO.sub.x) contained in a gas exhausted from the gas turbine.
A gas turbine plant or a combined cycle power generation plant generally includes a gas turbine combustor which burns a fuel gas, and a combustion gas from the combustor is fed to a gas turbine to drive the same. With the gas turbine of this character, it is known that the thermal efficiency of the turbine can be improved by increasing a temperature at an inlet port of the turbine, and for this purpose, in the known gas turbine plant, it is intended to increase the temperature at the inlet port of the turbine, i.e. temperature at an outlet port of the combustor.
However, it is impossible to increase a combustion gas temperature of the combustor without any restriction because of heat resisting limitation to materials constituting the gas turbine, combustor, etc. and countermeasure to NO.sub.x generated in the combustor.
The fuel and air are diffused, mixed and burned in the combustor, and under this condition, the generation of NO.sub.x is caused when the mixed gas with ratio of equivalency of the fuel and the air being near "1" at a temperature near the adiabatic flame temperature and the combustion gas in the combustor is locally highly heated.
In a known method for reducing the NO.sub.x generated in the gas turbine combustor, water vapor is introduced thereinto, and more in detail, in a single stage combustor in which fuel is introduced into the combustor through a fuel nozzle located at a top portion thereof, then diffused and burned, the water vapor is introduced into the combustor near the fuel nozzle to lower the temperature of the fuel gas, thus restricting the generation of the NO.sub.x.
As another NO.sub.x reducing method, there is known a diluted premix fuel combustion method in which the fed fuel is mixed with air having an amount more than that principally required to dilute evenly the mixed fuel gas and the thus diluted fuel gas is subjected to the premix combustion to prevent the fuel gas from locally highly heating and hence to restrict the generation of the NO.sub.x.
With the diluted premix fuel combustions method of this character, however, the combustion of the fuel is not stably carried out because of the use of the diluted premix fuel gas. In order to obviate this defect, a prior technique provides a gas turbine combustor which applies a two stage premix combustion method for stabilizing the combustion and in which a combustion chamber defined in the combustor liner is divided into two staged combustion areas. In the combustor of this two staged combustion type, the first combustion area disposed on the upstream side of the fuel gas is formed as a high temperature gas area wherein stable flame is generated by using a small amount of the first stage fuel and the diluted premix fuel gas, which is hardly flammable, in the second combustion area is then burned stably by the high temperature combustion gas generated in the first combustion area.
With the two stage premix combustor of this known type, however, it is necessary to carry out the diffusion-combustion mentioned before or combustion nearly the diffusion-combustion, so that there is a fear of generating the NO.sub.x having an amount approximately equal to that generated in the single stage combustor. Thus, the conventional two stage premix combustor has also a limitation to the restriction of the generation of the NO.sub.x.
In the known method of reducing the generation of the NO.sub.x in the gas turbine combustor by injecting the water vapor, a large amount of the water vapor is used because the vapor amount is determined in respect of the entire fuel flow amount, and in addition, there is a fear of generating harmful waste other than the NO.sub.x caused by impurities contained in the water vapor and a fear of corroding members or elements such as turbine blades by means of the impurities. In order to obviate these defects, the generation of the water vapor from pure water free from impurities is needed, which requires much cost and extra system. Nevertheless, the water vapor injected into the gas turbine combustor does not perform effective work such as steam in a steam turbine and exhausted into atmosphere as a part of the exhaust gas. With a combined cycle power plant in which a gas turbine and a steam turbine are operatively combined, the working efficiency of the power plant is relatively lowered by about 1% by the injection of the water vapor.
On the other hand, for the two stage premix combustor of the conventional type, since it is not required to inject the water vapor into the combustor, the generation of the NO.sub.x can be reduced without lowering the working efficiency of the plant.
However, with the conventional two stage premix combustor, no means is equipped to reduce the NO.sub.x generation, and accordingly, the combustor of this type has provided a problem for more effectively reducing the NO.sub.x generation. For example, the combined cycle power plant is equipped with a large sized denitrating device for reducing the harmful NO.sub.x in the combustion gas, and the installation of such a denitrating device requires much cost, thus providing a significant problem for the combined cycle power plant.